Efficient intracellular delivery of molecules such as drugs and/or nucleic acids (DNA, RNA and analogs) is critical for many therapies, and in particular for gene therapy. Efficient and finely localized intracellular delivery of nucleic acids is one of the most important stumbling blocks facing the practical use of gene therapy. Drug delivery methods can also benefit from an improvement in delivery efficiency and localization specificity.
Simply exposing cells to naked DNA results in relatively low transfection efficiencies. An article by Wolff et al. in Science 247:1465-1468 (Mar. 23, 1990), herein incorporated by reference, describes a method of direct gene transfer into mouse muscle cells. Pure DNA and RNA encoding reporter molecules (CAT or .beta.-galactosidase) were injected directly into mouse skeletal muscle. Approximately 1.5% of the .about.4000 muscle cells comprising the mouse quadriceps, and about 10-30% of the cells within the injection area were observed to display .beta.-galactosidase activity seven days after injection of 100 .mu.g of pRSVlac-Z DNA into individual quadriceps muscles. The method described by Wolff et al. is somewhat effective only for gene delivery to a limited injection area, and only in muscles. As indicated by Wolff et al., injection of pure DNA into other organs (liver, spleen, skin, lung, brain, and blood) results in much lower transfection efficiencies than injection in muscle. Also, the method described by Wolff et al. cannot be used to deliver DNA to large areas.
Higher transfection efficiencies can be achieved by coupling DNA to a delivery vehicle such as a liposome or a virus capsule. An article by Nabel et al. in Science 249:1285-1288 (Sep. 14, 1990), herein incorporated by reference, describes retroviral transfection and liposome-mediated transfection of arterial wall cells. The method allows site-specific gene transfer over a larger area than injection, but requires the use of potentially hazardous delivery vehicles. Such delivery vehicles are potentially toxic to the target cells, and can induce immunologic responses that can be harmful and/or reduce the effectiveness of gene transfer. Viral vectors are associated with risks of mutation and oncogenesis, and are not generally considered acceptable for widespread clinical applications.